Mechanical and Chemical-Mechanical planarization processes remove material from the surface of semiconductor wafers, field emission displays and many other microelectronic substrates to form a flat surface at a desired elevation in the substrates. FIG. 1 schematically illustrates a planarizing machine 10 with a platen 20, a carrier assembly 30, a polishing pad 40, and a planarizing solution 44 on the polishing pad 40. The planarizing machine 10 may also have a compressible under-pad 25 attached to an upper surface 22 of the platen 20 for supporting the polishing pad 40. In many planarizing machines, a drive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) the platen 20 to move the polishing pad 40 during planarization.
The carrier assembly 30 controls and protects a substrate 12 during planarization. The carrier assembly 30 generally has a lower surface 32 with a pad 34 that holds the substrate 12 via suction, and an actuator assembly 36 is typically attached to the carrier assembly 30 to rotate and/or translate the substrate 12 (arrows C and D, respectively). However, some carrier assemblies 30 are weighted, free-floating disks (not shown) that slide over the polishing pad 40.
The polishing pad 40 and the planarizing solution 44 may separately, or in combination, define a polishing environment that mechanically and/or chemically removes material from the surface of the substrate 12. The polishing pad 40 may be a conventional polishing pad made from a relatively compressible, porous continuous phase matrix material (e.g., polyurethane), or it may be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension medium. The planarizing solution 44 may be a chemical-mechanical planarization slurry with abrasive particles and chemicals for use with a conventional non-abrasive polishing pad, or the planarizing solution 44 may be a liquid without abrasive particles for use with an abrasive polishing pad. To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against a planarizing surface 42 of the polishing pad 40 in the presence of the planarizing solution 44. The platen 20 and/or the carrier assembly 30 then move relative to one another to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the polishing environment remove material from the surface of the substrate 12.
Planarizing processes must consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns on the substrate. As the density of integrated circuits increases, the uniformity and planarity of the substrate surface is becoming increasingly important because it is difficult to form sub-micron features or photo-patterns to within a tolerance of approximately 0.1 .mu.m when the substrate surface is not uniformly planar. Thus, planarizing processes must create a highly uniform, planar surface on the substrate.
In conventional planarizing processes, the substrate surface may not be uniformly planar because the rate at which material is removed from the substrate surface (the "polishing rate") typically varies from one region on the substrate to another. The polishing rate depends, in part, upon the distribution of abrasive particles and chemicals between the substrate surface and the polishing pad. One particular problem with conventional planarizing devices and methods is that the perimeter of the substrate wipes a significant amount of the planarizing solution off of the polishing pad. As such, the planarizing solution builds up in a high zone along a leading edge of the substrate, which reduces the volume of planarizing solution contacting the center of the substrate. Conventional planarizing devices and methods, therefore, typically produce a non-uniform, center-to-edge planarizing profile across the substrate surface.
To reduce such a center-to-edge planarizing profile, several conventional non-abrasive polishing pads have holes or grooves on their upper surfaces to transport a portion of the planarizing solution below the substrate surface during planarization. A Rodel IC-1000 polishing pad, for example, is a relatively soft, porous polyurethane pad with a number of large slurry wells approximately 0.05-0.10 inches in diameter that are spaced apart from one another across the planarization surface by approximately 0.125-0.25 inches. The large wells are expected to hold small volumes of slurry below the planarizing surface so that the substrate may draw the slurry out of the wells as the substrate translates over the pad. However, such pads still produce a significant center-to-edge planarizing profile indicating that the perimeter of the substrate presses some of the slurry out of the wells ahead of the center of the substrate. U.S. Pat. No. 5,216,843 describes another polishing pad with a plurality of macro-grooves formed in concentric circles and a plurality of micro-grooves radially crossing the macro-grooves. Although such grooves may improve the planarity of the substrate surface, substrates planarized with such pads still exhibit non-uniformities across the substrate surface indicating an inadequate distribution of planarizing solution and abrasive particles across the substrate.
Other types of polishing pads also do not adequately resolve the center-to-edge planarizing profile. For example, conventional porous polishing pads with small micro-pores at the planarizing surface are generally subject to producing a center-to-edge planarizing profile indicating that the perimeter of the substrate presses the planarizing solution out of the pores before the center of the substrate passes over the pores. Additionally, even fixed-abrasive polishing pads that have a uniform distribution of abrasive particles may produce a center-to-edge planarizing profile because the perimeter of the substrate also tends to sweep the planarizing solution off of abrasive polishing pads. Therefore, conventional polishing pads typically produce an undesired center-to-edge planarizing profile on the substrate surface.
To improve the distribution of slurry under the substrate, U.S. Pat. No. 5,489,233 discloses a polishing pad composed of a solid, uniform polymer sheet having no intrinsic ability to absorb or transport slurry particles. One type of polymer sheet disclosed in U.S. Pat. No. 5,489,233 is Mylar.RTM. manufactured by E.I. du Pont de Nemours of Wilmington, Del. The Polymer sheet has a surface pattern or texture that has both large and small flow channels to permit the transport of slurry across the surface of the polishing pad. The channels are mechanically produced on the pad. In a preferred embodiment, the pad has a macro-texture produced prior to planarization and a micro-texture produced by abrading the pad with a plurality of small abrasive points at regular selected intervals during planarization. Although the pad disclosed in U.S. Pat. No. 5,489,233 improves the uniformity of the substrate surface in some circumstances, it may not provide consistent planarization characteristics because scratching the surface with small abrasive points may not duplicate the micro-texture from one pad to the next. Thus, the polishing pad described in U.S. Pat. No. 5,489,233 may not provide consistent results from one substrate to the next.
Another factor affecting the uniformity of the substrate surface is the condition of the polishing pad. The planarizing surface of the polishing pad typically deteriorates after polishing a number of substrates because waste matter from the substrate, planarizing solution and/or the polishing pad accumulates on the planarizing surface. The waste matter alters the local planarizing characteristics of the pad, and the waste matter typically does not accumulate uniformly across the planarizing surface. Thus, the waste matter accumulations cause the polishing rate to vary across the surface of the polishing pad.
Polishing pads are accordingly "conditioned" by removing the waste matter from the pad to restore the polishing pad to a suitable condition for planarizing substrates. However, even conditioning polishing pads may produce non-uniformities in the substrate surface because it is difficult to consistently condition a polishing pad so that it has the same planarizing characteristics from one conditioning cycle to the next. Conditioning the polishing pads, moreover, is time-consuming and requires costly equipment and labor. Therefore, in addition to the problems associated with providing an adequate distribution of planarizing solution between the substrate surface and the polishing pad, conditioning conventional polishing pads may also reduce the uniformity of the planarized substrate surface.